As an additional thought, if you pull the NDS cranks you could temporarily swap the captain and stoker BB/crank/pedal assemblies (bike shoes too). If it moves to the stoker it’s in something that moved. If not, it’s something that stayed.
Those cranks look like they’ll require an allen to pull the screw, then a crank extractor ($15, Park has a how-to video on YouTube) to pull the arms. Alternatively you could also swap in self extracting crank arm bolts at about $15/pair if you think this will be happening a lot.